Both blocks are black, the 115hp 1150 I have is a 115hp! no questions on that one, the one I bought two weeks ago is the one in question, It is a black block I have not had time to check for any numbers on it, the guy I bought it from had it given to him, it does not have power trim or tilt and as far as I can tell matching up parts it looks to be a true 68-69 125.
The 1968-69 1250 was a silver block (that someone could have painted to be cute I suppose, [dunno why they would go to the trouble but stranger things could have happened, and probably have happened]).
The 1250 has old slyle twin fuel pumps on the side of the block that are very different from the single fuel pump system on yer 1975 1150 (or a 1400 or a 1500 fer that matter).
BTW: The blocks prior to 1971 0r 1972 do not bolt up to the later mid sections or visa versa so it is likely a painted silver block.
It is possible that 1250 carbs could have been put on a 1150 or a 1350. If they were jetted properly fer the application it could werk fine, (the big guns on this site would know the answer to that riddle), which is above my pay grade n' knowledge level.
If it is a 125 can i put that on my 115 mid section? and was it a good engine in its time?
If it is a 1968 0r 1969 silver block that was painted: NO. If it is a 1973 or later black block: YES, (unlikely due to the changed bolt pattern and the serial number you provided at the start of this thread). The 1250s were great engines, (I have two of 'em).
Also not sure what an exhaust tuner is, this is my first time with these engins
Go to a site with complete online parts catalog, (you will need to do this to figure out what yer FrankenMerc is anyhoooooo). Check the mid section picture from the online parts catalog fer yer 1975 1150 and your will see what an exhaust tuner is. (Try the sites listed at the sticky thread at the beginning of this section.)
The 1250s didn't have 'em yet my two 1969 1000s do, (the 100 hp engines were a smaller block [90 cubic inches] instead of the 100 cubic inch blocks we are talking about here).
Not sure if the 1350 had 'em, or the early 1970-71 silver block 1150 either (which can be made into a 1350 with carbs and maybe reeds), but all the black blocks I have owned have had them.
Thank you for your help